Specific Crystallographic Orientation Relationship Research Articles

Apatite formability of boron nitride nanotubes

This study investigates the ability of boron nitride nanotubes (BNNTs) to induce apatiteformation in a simulated body fluid environment for a period of 7, 14 and 28 days. BNNTs,when soaked in the simulated body fluid, are found to induce hydroxyapatite (HA)precipitation on their surface. The precipitation process has an initial incubation period of ∼ 4.6 days. The amount of HA precipitate increases gradually with the soaking time. Highresolution TEM results indicated a hexagonal crystal structure of HA needles. No specificcrystallographic orientation relationship is observed between BNNT and HA, which is dueto the presence of a thin amorphous HA layer on the BNNT surface that disturbs a definiteorientation relationship.

On the origin of oriented rutile needles in garnet from UHP eclogites

AbstractAlthough oriented rutile needles in garnet have been reported from several ultrahigh‐pressure (UHP) rocks and considered to be important UHP indicators, their crystallographic features including growth habit and lattice correspondences with garnet host have never been properly characterized. This paper presents a detailed analytical electron microscopic (AEM) study on evenly distributed oriented rutile needles in garnet of two eclogitic rocks from Sulu. Some garnet in one UHP diamondiferous quartzofeldspathic rock from the Saxonian Erzgebirge, and in one high‐pressure (HP) felsic granulite from Bohemia also contain a few unevenly distributed oriented rutile needles. They have also been studied for the purpose of comparison. Despite different distribution patterns, AEM revealed that all rutile needles are oriented along the 〈111〉 directions of garnet with their lateral sides surrounded by the {110} planes of garnet, and that the growth directions of most needles are close to the normal of the {101} planes of rutile. No other specific crystallographic orientation relationships between rutile and garnet host were observed, and there is no pyroxene associated with rutile, as necessitated by the precipitation reaction of rutile in garnet as previously proposed. A simple solid‐state precipitation scenario for the formation of the rutile needles in garnet in these two eclogitic rocks is not justified. Three alternative mechanisms are considered for the formation of oriented rutile needles: (i) the rutile needles may be inherited from precursor minerals; (ii) the rutile needles may be formed by a dissolution–reprecipitation mechanism; and (iii) the rutile needles may be formed by cleaving and healing of garnet with rutile deposition. None of these mechanisms can fully explain the observations, although the first one is less likely and the third one is preferred. This study presents an example where the presence of oriented/aligned inclusions in minerals does not necessarily imply a precipitation origin.

Structural property of β-FeSi 2 layers deposited on FeSi from a molten salt

The microstructural properties of the β-FeSi 2/FeSi structure prepared from a molten salt have been characterized using transmission electron microscopy (TEM). The β-FeSi 2 films were grown on FeSi substrates at the heat treatment temperature of 900 °C from 1 min to 24 h using the molten salt technique. It is found that the films consisted of a thin surface layer and a thick underlying layer with columnar-shaped domains. The crystallographic directions of the domains are mostly randomly oriented. The β-FeSi 2 domains in the film, however, have specific crystallographic orientation relationships with the adjoining domains and the FeSi substrate. A high density of the stacking faults on the β-FeSi 2 (100) planes was also observed through the films. Moreover, the growth evolution of the β-FeSi 2 domains, the defect characteristics and the formation mechanism of the defects are discussed.

Divorced eutectic and interface characteristics in a solidified YAG-spinel composite with spinel-rich composition

Solidified microstructures of YAG (Y3Al5O12)-spinel (MgAl2O4) composite with spinel-rich composition (YAG : spinel = 1 : 30 molar ratio) were investigated. Intergranular YAG divorced eutectic exhibiting fine-grained structures was observed in the solidified composite. Formation of the divorced eutectic was attributed to the metastable growth of primary phase spinel during solidification, which was verified by the presence of in situ spinel precipitates. TEM-SAD technique and crystal structure analysis reveal that a set of specific crystallographic orientation relationships are present between {640} plane of YAG and {111} plane of spinel crystals. The presence of low-energy YAG/spinel interfaces is believed to be responsible for the transgranular fracture characteristics exhibited for the solidified composite.

TEM Study of Microstructural Changes in an Anisotropic Nd–Fe–Co–B–Zr Magnet Alloy during HDDR Process

Changes in microstructure of Nd-Fe-Co-B-Zr alloy powder during the hydrogenation-decomposition-desorption-recombination (HDDR) process have been investigated in detail by transmission electron microscopy (TEM). It was found that the microstructural changes in the HDDR process start with the formation of cellular NdH2 and α-(Fe, Co) at a temperature between 933 and 973 K. The starting temperature is about 50 K higher than that of the Nd-Fe-B ternary system. By further annealing at 973 K, colonies of rod-shaped NdH2 and spherical grains of NdH2 grow, embedded in the α-(Fe, Co) matrix. It was confirmed by the selected area electron diffraction (SAED) analysis that there is no specific crystallographic orientation relationship between the original Nd2(Fe, Co) 14 B and the decomposed phases; NdH2 and α-(Fe, Co). (Fe, Co) 2 B grains appear above 973 K, but the number density of the grains is very small. These features suggest that none of the NdH2, the α-(Fe, Co) and the (Fe, Co)2B transfers the c-axis of the original Nd2(Fe, Co) 14 B to the recombined one. The microstructure formed at 1073-1103 K consists mainly of fine spherical NdH2 particles and α-(Fe, Co) matrix. Most of the NdH2 particles are covered with rims. The SAED and EDX analyses confirmed that the rim regions are made of Nd2 (Fe, Co) 14 B crystalline grains which are strongly correlated with one another in the crystal orientation. After a short treatment of hydrogen desorption, the rim-like phases grow up to form a microcrystalline structure of Nd 2 (Fe, Co) 14 B.